Thanks for the feedback man! I was thinking that the game might be too hard aswell, it's really hard to judge yourself when you've been playing it for so long (also not sure if you played with gamepad or not, I find it a lot easier with gamepad but it could just be my muscle memory). And yea you're right I should change the color for the boss at least. I'm too much of an artlet to do a new design for the boss though :D I find it really hard to balance the player projectiles. I initially had them cost mana but that makes it so that you can't use mana for anything else so I'm not sure I liked that solution.
I used a controller, I didn't try it with a keyboard. I don't play these types of games so my suggestion could be shit, but a thought that sprung to mind was to have the robot's ammo limited and replenish based on a timer (but honestly that wouldn't change my strategy, it'd just make me kite for longer).
Best of luck with whatever you come up with, I'd love to see a full game around this in the future! Some game progression would get me better acquainted with the other abilities and make me more likely to rely on them instead of just the one.